Problem: $ { \left[\begin{array}{rr}{-1} & {2} \\ {3} & {-1}\end{array}\right]+\left[\begin{array}{rr}{2} & {1} \\ {2} & {-2}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{2} & {2}+{1} \\ {3}+{2} & {-1}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{1} & {3} \\ {5} & {-3}\end{array}\right]}$